Spray Foam Insulation R-Value

You might get some sticker shock if you price out spray foam insulation.  It is expensive if done correctly by a professional contractor.  So, you want to make sure it’s worth it. Ideally, you want the highest R-value with the least material thickness and cost.

The way most insulation is measured and compared is by R-value.  The higher the number, the better at blocking the transfer of energy, or thermal resistance. There are three different spray foam insulations with different R-values per inch.

High-Density Most commonly used for roofing and exterior walls, high-density spray foam has an r-value that begins at 5.5 per inch— considered closed-cell at a density of 3 lbs per cubic foot.

Medium-Density Used for unvented attics and exterior and interior walls, medium-density spray foam has an r-value that begins at 5.7 per inch— considered closed-cell at a density of 2 lbs per cubic foot.

Low-Density Used in interior walls and unvented attics, low-density spray foam has an r-value that begins at 3.6 per inch— considered open-cell at a density of 0.5 lbs per cubic foot.

Problems with R-value of Spray Foam

Air leakage is the primary driver of energy efficiency as long as the insulation R-value is within range.  You can get the same performance from fiberglass as spray foam if your air, vapor, and R-values as the same.

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Problems with R-value of Spray Foam

So there is no significant difference in R-value when comparing the two types of spray foam in a stud wall.  Due to thermal bridging and open-cell foam covering the entire cavity.

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There is also Tripolymer spray foam. It is made with water-soluble materials.  It is usually used in existing buildings by injecting it into wall cavities.  While being injected, it will flow around objects and obstructions before it starts to expand and cure.

Third Type of Spray Foam – Tripolymer

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